This section endeavors to supply a context or background for the various exemplary embodiments of the invention as recited in the claims. The content herein may comprise subject matter that could be utilized, but not necessarily matter that has been previously utilized, described or considered. Unless indicated otherwise, the content described herein is not considered prior art, and should not be considered as admitted prior art by inclusion in this section.
It is widely known that the speed of propagation of interconnect signals is one of the most important factors controlling overall circuit speed as feature sizes are reduced and the number of devices per unit area increases. Throughout the semiconductor industry, there is a strong drive to reduce the dielectric constant (k) of the interlayer dielectric (ILD) materials such as those existing between metal lines, for example. As a result of such reduction, interconnect signals travel faster through conductors due to a concomitant reduction in resistance-capacitance (RC) delays.
Porous ultra low-k (ULK) dielectrics have enabled capacitance reduction in advanced silicon complementary metal-oxide semiconductor (CMOS) back end of line (BEOL) structures. However, the high level of porosity required (e.g., to achieve k values of 2.4 and lower) create issue in terms of dielectric material damage or loss due to plasma exposures (e.g., reactive ion etch (RIE), strip, dielectric barrier etch) and wet cleans (e.g., post RIE dilute hydrofluoric (DHF) cleans). Additionally, penetration of metals used in the liner layer (e.g., Ta, TaN) or the seed layer (e.g., Cu, Ru) into the pores of the dielectric can occur when porosity is high and the material is characterized by a high degree of pore connectivity. This leads to degradation of the dielectric break down strength and degradation of the leakage characteristics of the dielectric. All of these issues collectively cause reliability degradation in BEOL structures made using highly porous ULK dielectrics.
Various prior art techniques combat the above-identified issues in different manners. In one example, there are techniques to partially repair dielectric damage from plasma exposures. See, e.g., Y. S. Mor, T. C. Chang, P. T. Liu, T. M. Tsai, C. W. Chen, S. T. Yan, C. J. Chu, W. F. Wu, F. M. Pan, W. Lur, and S. M. Sze, “Effective repair to ultra-low-k dielectric material (k.apprx.2.0) by hexamethyldisilazane treatment,” J. Vac. Sci. Technol., B, vol. 20, pp. 1334-1338, 2002. In another example, there have been attempts to seal surface-connected pores to prevent metal penetration. See, e.g., R. J. O. M. Hoofman, V. H. Nguyen, V. Arnal, M. Broekaart, L. G. Gosset, W. F. A. Besling, M. Fayolle, and F. Iacopi, “Integration of low-k dielectric films in damascene processes,” in Dielectr. Films Adv. Microelectron., M. Baklanov, K. Maex, and M. Green, Eds. New-York: Wiley, 2007, pp. 199-250. However, these techniques require deposition of additional layers which can increase the effective dielectric constant of the integrated BEOL structure.